Multi-path analog front end and analog-to-digital converter for a signal processing system

ABSTRACT

A processing system may include multiple selectable processing paths for processing an analog signal in order to reduce noise and increase dynamic range. Techniques are employed to transition between processing paths and calibrate operational parameters of the two paths in order to reduce or eliminate artifacts caused by switching between processing paths.

RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional PatentApplication Ser. No. 61/948,307, filed Mar. 5, 2014, which isincorporated by reference herein in its entirety.

The present patent application is a continuation of a previously filedpatent application, U.S. patent application Ser. No. 14/476,507, filedSep. 3, 2014, the entirety of which is hereby incorporated by reference.

FIELD OF DISCLOSURE

The present disclosure relates in general to signal processing systems,and more particularly, to multiple path signal processing systems.

BACKGROUND

The use of multipath analog-to-digital converters (ADCs) and analogfront ends (AFEs) (e.g., two or more path ADCs/AFEs) in electricalcircuits is known. Example multipath ADCs and AFEs and use of them inmultiple electrical circuit paths are disclosed in U.S. Pat. No.5,714,956 entitled “Process and System for the Analog-to-DigitalConversion of Signals” to Jahne et al. (“Jahne patent”) and U.S. Pat.No. 5,600,317 entitled “Apparatus for the Conversion of Analog AudioSignals to a Digital Data Stream” to Knoth et al. (“Knoth patent”) andU.S. Pat. No. 6,271,780 entitled “Gain Ranging Analog-to-DigitalConverter with Error Correction” to Gong et al. (“Gong patent”). The useof multipath circuits may reduce noise as one path may be optimized forprocessing small amplitude signals (e.g., for processing low noisesignals) while another circuit path with another set of ADC and AFE isoptimized for large amplitude signals (e.g., allowing for higher dynamicrange).

An example application for multipath ADCs/AFEs is use of it in a circuitfor an audio system application, such as an audio mixing board or in adigital microphone system. Such an example application is disclosed inthe Jahne patent. In designing a circuit with multipath ADCs/AFEs thatare used in respective multiple circuit paths, a tradeoff may existbetween allowing larger signal swing (e.g., to allow swing of a signalbetween larger scale amplitudes) and low noise. Furthermore, themultipath ADCs/AFEs may provide high dynamic range signal digitization,with higher dynamic range for a given input power, and lower overallarea than would be possible with conventional means. In other words, byallowing a separate optimization for each type of signal (e.g., largeand small signals) that is provided each respective path, multipathADCs/AFEs allows the overall circuit to burn less power, consume lessarea, and save on other such design costs.

Despite their advantages, existing multipath ADC/AFE approaches havedisadvantages and problems. For example, many existing approaches havedisadvantages related to transitioning and switching between themultiple paths, as such switching may not be smooth, leading toundesirable signal artifacts, especially in audio applications in whichsuch artifacts may be perceptible to a listener of an audio device. Asanother example, a trend in electric circuits is to scale circuitry tothe integrated circuit level. However, existing approaches to multipathAFEs/ADCs do not scale well to the integrated circuit level.

SUMMARY

In accordance with the teachings of the present disclosure, certaindisadvantages and problems associated with implementation of a multipleAFE/ADC paths may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a processingsystem may include a plurality of processing paths and a controller. Theplurality of processing paths includes a first processing path and asecond processing path. The first processing path may comprise a firstanalog front end, and a first digital processing subsystem having afirst analog-to-digital converter, wherein the first analog front endincludes an inverting amplifier configured to amplify an analog inputsignal to generate a first amplified analog signal and the first digitalprocessing subsystem is configured to convert the first amplified analogsignal into a first digital signal. The second processing path maycomprise a second analog front end, and a second digital processingsubsystem having a second analog-to-digital converter, wherein thesecond analog front end includes a non-inverting amplifier configured toamplify the analog input signal to generate a second amplified analogsignal and the digital processing subsystem is configured to convert thesecond amplified analog signal into a second digital signal. Thecontroller may be configured to select one of the first digital signaland the second digital signal as a digital output signal of theprocessing system based on a magnitude of the analog input signal.

In accordance with these and other embodiments of the presentdisclosure, a processing system may include a plurality of processingpaths and a controller. The plurality of processing paths may include afirst processing path and a second processing path. The first processingpath may comprise a first analog front end and a first digitalprocessing subsystem having a first analog-to-digital converter, whereinthe first analog front end is configured to amplify an analog inputsignal in order to generate a first amplified analog signal and thefirst analog-to-digital converter is configured to convert the firstamplified analog signal into a first digital signal. The secondprocessing path may comprise a second analog front end and a seconddigital processing subsystem having a second analog-to-digitalconverter, wherein the second analog front end is configured to amplifythe analog input signal to generate a second amplified analog signal andthe second analog-to-digital converter is configured to convert thesecond amplified analog signal into a second digital signal, and furtherwherein a magnitude of the gain of the second analog front end issubstantially larger than a magnitude of a gain of the first analogfront end. The controller may be configured to select one of the firstdigital signal and the second digital signal as a digital output signalof the processing system based on a magnitude of the analog inputsignal. The controller may also be configured to, when selecting thefirst digital signal as the digital output signal, transitioncontinuously or in steps the digital output signal between the seconddigital signal and the first digital signal during a duration of time,such that during such transition, the digital output signal is aweighted average of the first digital signal and the second digitalsignal wherein a weight of the first digital signal relative to a weightof the second digital signal increases during such transition. Thecontroller may further be configured to, when selecting the seconddigital signal as the digital output signal, transition continuously orin steps the digital output signal between the first digital signal andthe second digital signal, wherein a rate of transition is based on themagnitude of the analog input signal, and such that during suchtransition, the digital output signal is a weighted average of the firstdigital signal and the second digital signal wherein a weight of thesecond digital signal relative to a weight of the first digital signalincreases during the transition.

In accordance with these and other embodiments of the presentdisclosure, a processing system may include a plurality of processingpaths and a controller. The plurality of processing paths may include afirst processing path and a second processing path. The first processingpath may comprise a first analog front end and a first digitalprocessing subsystem having a first analog-to-digital converter, whereinthe first analog front end is configured to amplify an analog inputsignal in order to generate a first amplified analog signal and thefirst analog-to-digital converter is configured to convert the firstamplified analog signal into a first digital signal, and further whereinthe first analog-to-digital converter comprises a first modulatorconfigured to receive the first amplified input signal and a firstdigital decimator configured to receive an output of the firstmodulator. The second processing path may comprise a second analog frontend and a second digital processing subsystem having a secondanalog-to-digital converter, wherein the second analog front end isconfigured to amplify the analog input signal to generate a secondamplified analog signal and the second analog-to-digital converter isconfigured to convert the second amplified analog signal into a seconddigital signal, further wherein the second analog-to-digital convertercomprises a second modulator configured to receive the second amplifiedinput signal and a second digital decimator configured to receive anoutput of the second modulator, and further wherein a magnitude of thegain of the second analog front end is substantially larger than amagnitude of a gain of the first analog front end. The controller may beconfigured to switch selection from the second digital signal to thefirst digital signal based on the output of the second modulator.

In accordance with these and other embodiments of the presentdisclosure, a processing system may include a plurality of processingpaths and a controller. The plurality of processing paths may include afirst processing path and a second processing path. The first processingpath may have a first path gain and may be configured to generate afirst analog signal based on an analog input signal. The secondprocessing path may have a second path gain and may be configured togenerate a second analog signal based on the analog input signal. Thecontroller may be configured to select one of the first digital signaland the second digital signal as a digital output signal of theprocessing system based on a magnitude of the analog input signal,determine a scale factor indicative of the magnitude of differencebetween the first path gain and the second path gain, and prior toswitching selection between the first digital signal and the seconddigital signal, apply an additional gain based on the scale factor toone or both of the first path gain and the second path gain tocompensate for the magnitude of difference between the first path gainand the second path gain.

In accordance with these and other embodiments of the presentdisclosure, a method may include processing an analog input signal witha first processing path, wherein the first processing path comprises afirst analog front end, and a first digital processing subsystem havinga first analog-to-digital converter, wherein the first analog front endincludes an inverting amplifier configured to amplify the analog inputsignal to generate a first amplified analog signal and the first digitalprocessing subsystem is configured to convert the first amplified analogsignal into a first digital signal. The method may also includeprocessing the analog input signal with a second processing path,wherein the second processing path comprises a second analog front end,and a second digital processing subsystem having a secondanalog-to-digital converter, wherein the second analog front endincludes a non-inverting amplifier configured to amplify the analoginput signal to generate a second amplified analog signal and thedigital processing subsystem is configured to convert the secondamplified analog signal into a second digital signal. The method mayfurther include selecting one of the first digital signal and the seconddigital signal as a digital output signal of the processing system basedon a magnitude of the analog input signal.

In accordance with these and other embodiments of the presentdisclosure, a method may include processing an analog input signal witha first processing path, wherein the first processing path comprises afirst analog front end and a first digital processing subsystem having afirst analog-to-digital converter, wherein the first analog front end isconfigured to amplify the analog input signal in order to generate afirst amplified analog signal and the first analog-to-digital converteris configured to convert the first amplified analog signal into a firstdigital signal. The method may also include processing the analog inputsignal with a second processing path, wherein the second processing pathcomprises a second analog front end and a second digital processingsubsystem having a second analog-to-digital converter, wherein thesecond analog front end is configured to amplify the analog input signalto generate a second amplified analog signal and the secondanalog-to-digital converter is configured to convert the secondamplified analog signal into a second digital signal, and furtherwherein a magnitude of the gain of the second analog front end issubstantially larger than a magnitude of a gain of the first analogfront end. The method may further include selecting one of the firstdigital signal and the second digital signal as a digital output signalof the processing system based on a magnitude of the analog inputsignal. The method may additionally include, when selecting the firstdigital signal as the digital output signal, transitioning continuouslyor in steps the digital output signal between the second digital signaland the first digital signal during a duration of time, such that duringsuch transition, the digital output signal is a weighted average of thefirst digital signal and the second digital signal wherein a weight ofthe first digital signal relative to a weight of the second digitalsignal increases during such transition. The method may also include,when selecting the second digital signal as the digital output signal,transitioning continuously or in steps the digital output signal betweenthe first digital signal and the second digital signal, wherein a rateof transition is based on the magnitude of the analog input signal, andsuch that during such transition, the digital output signal is aweighted average of the first digital signal and the second digitalsignal wherein a weight of the second digital signal relative to aweight of the first digital signal increases during the transition.

In accordance with these and other embodiments of the presentdisclosure, a method may include processing an analog input signal witha first processing path, wherein the first processing path comprises afirst analog front end and a first digital processing subsystem having afirst analog-to-digital converter, wherein the first analog front end isconfigured to amplify the analog input signal in order to generate afirst amplified analog signal and the first analog-to-digital converteris configured to convert the first amplified analog signal into a firstdigital signal, and further wherein the first analog-to-digitalconverter comprises a first modulator configured to receive the firstamplified input signal and a first digital decimator configured toreceive an output of the first modulator. The method may also includeprocessing the analog input signal with a second processing path,wherein the second processing path comprises a second analog front endand a second digital processing subsystem having a secondanalog-to-digital converter, wherein the second analog front end isconfigured to amplify the analog input signal to generate a secondamplified analog signal and the second analog-to-digital converter isconfigured to convert the second amplified analog signal into a seconddigital signal, further wherein the second analog-to-digital convertercomprises a second modulator configured to receive the second amplifiedinput signal and a second digital decimator configured to receive anoutput of the second modulator, and further wherein a magnitude of thegain of the second analog front end is substantially larger than amagnitude of a gain of the first analog front end. The method mayfurther include switching selection from the second digital signal tothe first digital signal based on the output of the second modulator.

In accordance with these and other embodiments of the presentdisclosure, a method may include processing an analog input signal by afirst processing path having a first path gain and configured togenerate a first analog signal based on an analog input signal. Themethod may also include processing the analog input signal by a secondprocessing path having a second path gain and configured to generate asecond analog signal based on the analog input signal. The method mayfurther include selecting one of the first digital signal and the seconddigital signal as a digital output signal of the processing system basedon a magnitude of the analog input signal. The method may additionallyinclude determining a scale factor indicative of the magnitude ofdifference between first path gain and second path gain. The method mayalso include, prior to switching selection between the first digitalsignal and the second digital signal, applying an additional gain basedon the scale factor to one or both of the first path gain and the secondpath gain to compensate for the magnitude of difference between thefirst path gain and the second path gain.

Technical advantages of the present disclosure may be readily apparentto one having ordinary skill in the art from the figures, descriptionand claims included herein. The objects and advantages of theembodiments will be realized and achieved at least by the elements,features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are explanatory examples and are notrestrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates a block diagram of selected components of an examplesignal processing system, in accordance with embodiments of the presentdisclosure;

FIG. 2 illustrates a block diagram of selected components of anintegrated circuit for processing an analog signal to generate a digitalsignal, in accordance with embodiments of the present disclosure; and

FIG. 3 illustrates a block diagram of selected components of theintegrated circuit of FIG. 2 depicting selected components of exampleembodiments of analog front ends and analog-to-digital converters, inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a block diagram of selected components of an examplesignal processing system 100, in accordance with embodiments of thepresent disclosure. As shown in FIG. 1, signal processing system 100 mayinclude an analog signal source 101, an integrated circuit (IC) 105, anda digital processor 109. Analog signal source 101 may comprise anysystem, device, or apparatus configured to generate an analog electricalsignal, for example an analog input signal ANALOG_IN. For example, inembodiments in which signal processing system 100 is a processingsystem, analog signal source may comprise a microphone transducer.

Integrated circuit 105 may comprise any suitable system, device, orapparatus configured to process analog input signal ANALOG_IN togenerate a digital output signal DIGITAL_OUT and condition digitaloutput signal DIGITAL_OUT for transmission over a bus to digitalprocessor 109. Once converted to digital output signal DIGITAL_OUT, thesignal may be transmitted over significantly longer distances withoutbeing susceptible to noise as compared to an analog transmission overthe same distance. In some embodiments, integrated circuit 105 may bedisposed in close proximity with analog signal source 101 to ensure thatthe length of the analog line between analog signal source 101 andintegrated circuit 105 is relatively short to minimize the amount ofnoise that can be picked up on an analog output line carrying analoginput signal ANALOG_IN. For example, in some embodiments, analog signalsource 101 and integrated circuit 105 may be formed on the samesubstrate. In other embodiments, analog signal source 101 and integratedcircuit 105 may be formed on different substrates packaged within thesame integrated circuit package.

Digital processor 109 may comprise any suitable system, device, orapparatus configured to process digital output signal for use in adigital system. For example, digital processor 109 may comprise amicroprocessor, microcontroller, digital signal processor (DSP),application specific integrated circuit (ASIC), or any other deviceconfigured to interpret and/or execute program instructions and/orprocess data, such as digital output signal DIGITAL_OUT.

Signal processing system 100 may be used in any application in which itis desired to process an analog signal to generate a digital signal.Thus, in some embodiments, signal processing system 100 may be integralto an audio device that converts analog signals (e.g., from amicrophone) to digital signals representing the sound incident on amicrophone. As another example, signal processing system 100 may beintegral to a radio-frequency device (e.g., a mobile telephone) toconvert radio-frequency analog signals into digital signals.

FIG. 2 illustrates a block diagram of selected components of integratedcircuit 105, in accordance with embodiments of the present disclosure.As shown in FIG. 2, integrated circuit 105 may include two or moreprocessing paths 201 a and 201 b (which may be referred to hereinindividually as a processing path 201 and collectively as processingpaths 201), each processing path 201 including a respective AFE 203(e.g., AFE 203 a, AFE 203 b) and a respective ADC (e.g., ADC 215 a, ADC215 b). An AFE 203 may receive analog input signal ANALOG_IN via one ormore input lines which may allow for receipt of a single-ended signal,differential signal, or any other suitable analog signal format and maycomprise any suitable system, device, or apparatus configured tocondition analog input signal ANALOG_IN for processing by ADC 215.Selected components for example embodiments of AFEs 203 a and 203 b arediscussed in greater detail below with respect to FIG. 3. The output ofeach AFE 203 may be communicated to a respective ADC 215 on one or moreoutput lines.

An ADC 215 may comprise any suitable system, device, or apparatusconfigured to convert an analog signal received at its input, to adigital signal representative of analog input signal ANALOG_IN. ADC 215may itself include one or more components (e.g., delta-sigma modulator,decimator, etc.) for carrying out the functionality of ADC 215. Selectedcomponents for the example embodiments of ADCs 215 a and 215 b arediscussed in greater detail below with respect to FIG. 3.

A multiplexer 227 may receive a respective digital signal from each ofprocessing paths 201 and may select one of the digital signals asdigital output signal DIGITAL_OUT based on a control signal generated byand communicated from a controller 220.

Driver 219 may receive the digital signal DIGITAL_OUT output by ADC 215and may comprise any suitable system, device, or apparatus configured tocondition such digital signal (e.g., encoding into Audio EngineeringSociety/European Broadcasting Union (AES/EBU), Sony/Philips DigitalInterface Format (S/PDIF)), in the process generating digital outputsignal DIGITAL_OUT for transmission over a bus to digital processor 109.In FIG. 2, the bus receiving digital output signal DIGITAL_OUT is shownas single-ended. In some embodiments, driver 219 may generate adifferential digital output signal 107.

Controller 220 may comprise any suitable system, device, or apparatusfor selecting one of the digital signals output by the variousprocessing paths 201 as digital output signal DIGITAL_OUT. In someembodiments, controller 220 may make such selection based on a magnitudeof analog input signal ANALOG_IN or a signal derivative thereof. Forexample, controller 220 may include an overload detector 221 that maydetermine whether or not a signal derivative of analog input signalANALOG_IN (e.g., an output of a modulator 316 a of delta-sigma modulator308 a, as shown in greater detail in FIG. 3) is likely to cause clippingor other distortion of digital output signal DIGITAL_OUT if a particularprocessing path (e.g., processing path 201 a) is selected. If clippingor other distortion of digital output signal DIGITAL_OUT is likely ifthe particular processing path (e.g., processing path 201 a) isselected, state machine 225 of controller 220 may generate a controlsignal so that another processing path (e.g., processing path 201 b) isselected. To further illustrate, in some embodiments, processing path201 a may be a path adapted for low amplitudes of analog input signalANALOG_IN and may thus have a high signal gain, while processing path201 b may be a path adapted for higher amplitudes of analog input signalANALOG_IN and may thus have a lower signal gain. Thus, if analog inputsignal ANALOG_IN or a derivative thereof is greater than a thresholdvalue indicative of a condition whereby digital output signalDIGITAL_OUT may experience clipping or other distortion if processingpath 201 a is selected, overload detector 221 may detect such condition,and cause state machine 225 to generate a control signal to select thedigital signal generated by processing path 201 b as digital outputsignal DIGITAL_OUT.

As another example, controller 220 may include a level detector 223 thatmay detect an amplitude of analog input signal ANALOG_IN or a signalderivative thereof (e.g., a signal generated within ADC 215 b) andcommunicate a signal indicative of such amplitude to state machine 225.Responsive to the signal received from level detector 223, state machine225 may generate the control signal communicated to multiplexer 227. Toillustrate, as analog input signal ANALOG_IN decreases from a relativelyhigh amplitude to a lower amplitude, it may cross a threshold amplitudelevel whereby controller 220 may change the selection of digital outputsignal DIGITAL_OUT from the digital signal generated by processing path201 b (which may be adapted for higher amplitudes of analog input signalANALOG_IN) to the digital signal generated by processing path 201 a(which may be adapted for lower amplitudes of analog input signalANALOG_IN). In some embodiments, a threshold amplitude level wherebycontroller 220 may change the selection of digital output signalDIGITAL_OUT from the digital signal generated by processing path 201 bto the digital signal generated by processing path 201 a may be lowerthan another threshold amplitude level whereby controller 220 may changethe selection of digital output signal DIGITAL_OUT from the digitalsignal generated by processing path 201 a to the digital signalgenerated by processing path 201 b, in order to provide for hysteresisso that multiplexer 227 does not repeatedly switch between the paths.

FIG. 3 illustrates a block diagram of selected components of integratedcircuit 105 depicting selected components of example embodiments of AFEs203 and ADCs 215, in accordance with embodiments of the presentdisclosure. As shown in FIG. 3, analog front end 203 a of processingpath 201 a may include a high-pass filter 302 configured to high-passfilter analog input signal ANALOG_IN to remove direct current offsets orbiases, which are often particularly troublesome for high-gainamplifiers, and output such filtered signal to a non-inverting amplifier304. Non-inverting amplifier 304 may amplify analog input signalANALOG_IN by a non-inverting gain and communicate such amplified analogsignal to ADC 215 a. In some embodiments, high-pass filter 302 may beformed on the same integrated circuit as one or more of AFE 203 a, AFE203 b, ADC 215 a, and ADC 215 b. Because of the presence of high-passfilter 302 in processing path 201 a, but not processing path 201 b,processing paths 201 may each have a different frequency response toanalog input signal ANALOG_IN.

Also as shown in FIG. 3, analog front end 203 b of processing path 201 bmay include an inverting amplifier 306 which may amplify analog inputsignal ANALOG_IN by an inverting gain and communicate such amplifiedanalog signal to ADC 215 b. In some embodiments, inverting amplifier 306may be configured to apply a multiplicative gain of less than unity toanalog input signal ANALOG_IN. By attenuating higher-amplitude signals,a greater dynamic range for analog input signal ANALOG_IN may beachieved, in spite of conventional wisdom that would generally dictatethat signal loss should be avoided in a low-noise system. In these andother embodiments, although not depicted in FIG. 3, inverting amplifier306 may receive the output of high-pass filter 302 instead of theunfiltered analog input signal ANALOG_IN.

Although AFEs 203 a and 203 b are described above having a non-invertinggain and an inverting gain, respectively, each of processing paths 201may have approximately the same cumulative gain. Those of skill in theart may appreciate that simply applying a digital gain with a negativesign in either of ADC 215 a or ADC 215 b will negate the oppositepolarities of the gains of AFEs 203.

As depicted in FIG. 3, each ADC 215 may include a respective delta-sigmamodulator 308 (e.g., delta-sigma modulators 308 a and 308 b), arespective digital gain element 310 (e.g., digital gain elements 310 aand 310 b), and respective high-pass filters 312 (e.g., high-passfilters 312 a and 312 b). Each delta-sigma modulator 308 may beconfigured to modulate an analog signal into a corresponding digitalsignal. As known in the art, each delta-sigma modulator 308 may includea respective modulator 316 (e.g., modulators 316 a, 316 b) and adecimator 318 (e.g., decimators 318 a, 318 b). Each digital gain element310 may apply a gain to a digital signal generated by its associateddelta-sigma modulator 308. Each high-pass filter 312 may high-passfilter a digital signal generated by its associated digital gainelement, to filter out any direct-current offsets present in the digitalsignal. High-pass filter 312 b may also compensate for high-pass filter302 present in AFE 203 a.

In addition, ADC 215 a may comprise a latency matching element 314 tomatch any signal latencies between processing path 201 a and processingpath 201 b, while ADC 215 b may comprise a phase matching element 316 toaccount for any phase offset between processing path 201 a andprocessing path 201 b. For example, phase matching element 316 maydynamically compensate for any phase mismatch between processing paths201 a and 201 b by varying a delay of at least one of processing path201 a and processing path 201 b. In some embodiments, phase matchingelement 316 may comprise a high-pass filter.

In some embodiments, a magnitude of a gain of non-inverting amplifier304 may be substantially larger than (e.g., significantly more thanmanufacturing tolerances, one or more orders of magnitude) a magnitudeof a gain of inverting amplifier 306. In addition, in these and otherembodiments, a magnitude of digital gain element 310 b may besubstantially larger than (e.g., significantly more than manufacturingtolerances, one or more orders of magnitude) a magnitude of a gain ofdigital gain element 310 a. Consequently, in such embodiments, a firstpath gain equal to the product of the magnitude of the gain of invertingamplifier 306 and the magnitude of a gain of digital gain element 310 bmay be substantially equal (e.g., within manufacturing tolerances) to asecond path gain equal to the product of the magnitude of gain ofnon-inverting amplifier 304 and the gain of digital gain element 310 a.As a specific example, in some embodiments, the inverting gain ofinverting amplifier 306 may be approximately −6 decibels, thenon-inverting gain of non-inverting amplifier 304 may be approximately20 decibels, the gain of digital gain element 310 a may be approximately−26 decibels, and the gain of digital gain element 310 b may beapproximately 0 decibels.

Accordingly, each processing path 201 may be adapted to process aparticular amplitude of analog input signal ANALOG_IN. For example, AFE203 a may be suited to process lower signal amplitudes, as non-invertingamplifier 304 may have a practically infinite input resistance, may havea relatively low level of input-referred noise as compared to invertingamplifier 306, and its larger gain may permit effective processing ofsmaller signals, but characteristics of AFE 203 a may not be amenable tohigher amplitudes. The high input resistance of non-inverting amplifier304 may facilitate the use of a smaller capacitor area for high-passfilter 302 (as compared to traditional approaches for implementinghigh-pass filters) and thus may permit integration of circuitry ofhigh-pass filter 302 into the same integrated circuit as non-invertingamplifier 304, inverting amplifier 306, ADC 215 a, and/or ADC 215 b. Inaddition, the ability to integrate circuitry into a single integratedcircuit may allow for centralized control of the stimuli for switchingbetween processing paths 201 by controller 220, and may allow for moredirect timing control of the actual switching and transitioning betweenprocessing paths 201. For example, because circuitry is integrated intoa single integrated circuitry, level detector 223 may receive an outputof delta-sigma modulator 308 b as an input signal, rather than receivingan output of ADC 215 b.

On the other hand, AFE 203 b may be suited to process higher signalamplitudes, as its lower gain will reduce the likelihood of signalclipping, and may provide for greater dynamic range for analog inputsignal ANALOG_IN as compared to traditional approaches.

Despite a designer's best efforts to match the first path gain and thesecond path gain, process variations, temperature variations,manufacturing tolerances, and/or other variations may lead to the firstpath gain and the second path gain being unequal. If switching betweenpaths occurs when such path gains are unequal, signal artifacts mayoccur due to an instantaneous, discontinuous change in magnitude of thedigital output signal between two gain levels. For example, in audiosignals, such artifacts may include human-perceptible “pops” or “clicks”in acoustic sounds generated from audio signals.

In some embodiments, in order to reduce or eliminate the occurrence ofsuch artifacts when switching selection between the digital outputsignal of ADC 215 a and the digital output signal of ADC 215 b, and viceversa, controller 220 may program an additional gain into one or both ofprocessing paths 201 to compensate for differences in the first pathgain and second path gain. This additional gain factor may equalize thefirst path gain and the second path gain To illustrate, controller 220may determine a scale factor indicative of the magnitude of difference(e.g., whether an intentional difference or unintentional mismatch)between first path gain of processing path 201 a and the second pathgain of processing path 201 b. The controller may determine first pathgain and the second path gain by comparing the digital output signals ofeach processing path to analog input signal ANALOG_IN or a derivativethereof. If such digital output signals have been filtered by ahigh-pass filter (e.g., high-pass filters 312), a direct-current offsetbetween the signals may be effectively filtered out, which may benecessary to accurately compute the relative path gains. Controller 220may determine the scale factor by calculating one of a root mean squareaverage of the first path gain and the second path gain and a least meansquares estimate of the difference between the first path gain and thesecond path gain. Prior to switching selection between the first digitalsignal generated by ADC 215 a and the second digital signal generated byADC 215 b (or vice versa), controller 220 may program an additional gaininto one of processing paths 201 to compensate for the gain differenceindicated by the scale factor. For example, controller 220 may calibrateone or both of the first path gain and the second path gain by applyinga gain equal to the scale factor or the reciprocal of the gain factor(e.g., 1/gain factor), as appropriate. Such scaling may be performed bymodifying one or both of digital gains 310. In some embodiments,controller 220 may apply the additional gain to the processing path 201of the digital signal not selected as digital output signal DIGITAL_OUT.For example, controller 220 may apply the additional gain to processingpath 201 a when the digital signal of ADC 215 b is selected as digitaloutput signal DIGITAL_OUT and apply the additional gain to processingpath 201 b when the digital signal of ADC 215 a is selected as digitaloutput signal DIGITAL_OUT.

In some embodiments, the additional gain, once applied to a path gain ofa processing path 201, may be allowed over a period of time to approachor “leak” to a factor of 1, in order to constrain the additional gainand compensate for any cumulative (e.g., over multiple switching eventsbetween digital signals of ADCs 215) bias in the calculation of theadditional gain. Without undertaking this step to allow the additionalgain to leak to unity, multiple switching events between paths may causethe gain factor to increase or decrease in an unconstrained manner assuch additional gain, if different than unity, affects the outputs ofthe multiple paths and thus affects the calculation of the scalingfactor.

In some embodiments, switching selection of digital output signalDIGITAL_OUT from the digital signal of ADC 215 a to the digital signalof ADC 215 b (or vice versa), may occur substantially immediately.However, in some embodiments, to reduce or eliminate artifacts fromoccurring when switching selection of digital output signal DIGITAL_OUTfrom the digital signal of ADC 215 a to the digital signal of ADC 215 b(or vice versa), controller 220 and multiplexer 227 may be configured totransition continuously or in steps digital output signal DIGITAL_OUTfrom a first digital signal to a second digital signal such that duringsuch transition, digital output signal DIGITAL_OUT is a weighted averageof the first digital signal and the second digital signal wherein aweight of the second digital signal relative to a weight of the firstdigital signal increases during the transition. For example, if atransition is desired between digital signal of ADC 215 a and digitalsignal of ADC 215 b as digital output signal DIGITAL_OUT, suchtransition may be in steps, wherein in each step, controller 220 and/ormultiplexer 227 weighs digital signals output by ADCs 215 as follows:

1) 100% digital signal of ADC 215 a and 0% digital signal of ADC 215 b;

2) 80% digital signal of ADC 215 a and 20% digital signal of ADC 215 b;

3) 60% digital signal of ADC 215 a and 40% digital signal of ADC 215 b;

4) 30% digital signal of ADC 215 a and 70% digital signal of ADC 215 b;

5) 10% digital signal of ADC 215 a and 90% digital signal of ADC 215 b;and

6) 0% digital signal of ADC 215 a and 100% digital signal of ADC 215 b.

As another example, if a transition is desired between digital signal ofADC 215 b and digital signal of ADC 215 a as digital output signalDIGITAL_OUT, such transition may be in steps, wherein in each step,controller 220 and/or multiplexer 227 weighs digital signals output byADCs 215 as follows:

1) 100% digital signal of ADC 215 b and 0% digital signal of ADC 215 a;

2) 70% digital signal of ADC 215 b and 30% digital signal of ADC 215 a;

3) 60% digital signal of ADC 215 b and 40% digital signal of ADC 215 a;

4) 20% digital signal of ADC 215 b and 80% digital signal of ADC 215 a;

5) 5% digital signal of ADC 215 b and 95% digital signal of ADC 215 a;and

6) 0% digital signal of ADC 215 b and 100% digital signal of ADC 215 a.

In some embodiments, a transition in digital output signal DIGITAL_OUT(either continuously or in steps) from the digital signal of ADC 215 ato the digital signal of ADC 215 b (or vice versa) may occur over adefined maximum duration of time. In these and other embodiments, whentransitioning (either continuously or in steps) digital output signalDIGITAL_OUT from the digital signal of ADC 215 b to the digital signalof ADC 215 a, a rate of transition may be based on a magnitude of analoginput signal ANALOG_IN (e.g., the rate of transition may be faster atlower amplitudes and slower at higher amplitudes). In such embodiments,the minimum rate of such transition may be limited such that thetransition occurs over a defined maximum duration of time, wherein themaximum duration of time is independent of the magnitude of the analoginput signal.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

The invention claimed is:
 1. A processing system comprising: a pluralityof processing paths including a first processing path and a secondprocessing path, wherein: the first processing path has a first pathgain and is configured to generate a first analog signal based on ananalog input signal; and the second processing path has a second pathgain and is configured to generate a second analog signal based on theanalog input signal; and a controller configured to: select one of thefirst digital signal and the second digital signal as a digital outputsignal of the processing system based on a magnitude of the analog inputsignal; determine a scale factor indicative of the magnitude ofdifference between first path gain and second path gain; and prior toswitching selection between the first digital signal and the seconddigital signal, apply an additional gain based on the scale factor toone or both of the first path gain and the second path gain tocompensate for the magnitude of difference between the first path gainand the second path gain.
 2. The processing system of claim 1, whereinthe controller is configured to determine the scale factor bycalculating one of a root mean square average of the first path gain andthe second path gain and a least mean squares estimate of the differencebetween the first path gain and the second path gain.
 3. The processingsystem of claim 1, wherein the controller applies the additional gain tothe first processing path if the second digital signal is selected asthe digital output signal and applies the additional gain to the secondprocessing path if the first digital signal is selected as the digitaloutput signal.
 4. The processing system of claim 1, wherein thecontroller applies the additional gain to the first processing path if aselection of the digital output signal switches between the seconddigital signal to the first digital signal and applies the additionalgain to the second processing path if a selection of the digital outputsignal switches between the first digital signal to the second digitalsignal.
 5. The processing system of claim 1, wherein the processingsystem is an audio processing system, and the analog input signal andthe digital output signal are each an audio signal.
 6. A methodcomprising: processing an analog input signal by a first processing pathhaving a first path gain and configured to generate a first analogsignal based on an analog input signal; processing the analog inputsignal by a second processing path having a second path gain andconfigured to generate a second analog signal based on the analog inputsignal; selecting one of a first digital signal and a second digitalsignal as a digital output signal of a processing system based on amagnitude of the analog input signal; determining a scale factorindicative of the magnitude of difference between first path gain andsecond path gain; and prior to switching selection between the firstdigital signal and the second digital signal, applying an additionalgain based on the scale factor to one or both of the first path gain andthe second path gain to compensate for the magnitude of differencebetween the first path gain and the second path gain.
 7. The method ofclaim 6, further comprising determining the scale factor by calculatingone of a root mean square average of the first path gain and the secondpath gain and a least mean squares estimate of the difference betweenthe first path gain and the second path gain.
 8. The method of claim 6,further comprising applying the additional gain to the first processingpath if the second digital signal is selected as the digital outputsignal and applying the additional gain to the second processing path ifthe first digital signal is selected as the digital output signal. 9.The method of claim 6, further comprising applying the additional gainto the first processing path if a selection of the digital output signalswitches between the second digital signal to the first digital signaland applying the additional gain to the second processing path if aselection of the digital output signal switches between the firstdigital signal to the second digital signal.
 10. The method of claim 6,wherein the analog input signal and the digital output signals are eachan audio signal.